I know this question is a year old, but Microsoft sells replacement feet for £4.80 in the UK outside of warranty. To purchase a pair head to:
* Microsoft account | Devices
* Select your Surface Laptop
* Select Start Service Online
* Select Accessory | Misc
* Describe that you need replacement feet
* Choose from the colour you need
* Select your address
* Pay
I encountered a cookies issue that prevented me from paying, but it worked after 2/3 tries.